Apple 1 Basic Manual

PRELIMINARY
APPLE BASIC USERS MANUAL
OCTOBER 19 76

Apple Computer Company • 770 Welch Rd., Palo Alto, CA 94304 • (415) 326-4248

This is a PRELIMINARY manual. It will, most likley, contain

errors, incorrect wordings, etc. Your effort in noting these

areas of improvement will be greatly appreciated.

If you find an error or can suggest an improvement, please

write:

APPLE COMPUTER COMPANY

770 WELCH RD. SUITE 154

PALO ALTO, CA 94304

(415) 326-4248

LOADING APPLE BASIC

Apple BASIC is provided on a cassette tape which can be read into
the "Elf block of memory in about 30 seconds. To load BASIC from
the tape do the following:

Hit the "CLEAR SCREEN" button which will clear the screen
and display only the cursor (a flashing @ sign) in the
upper left corner of the screen.

Hit the "RESET" button which will cause the computer to print
a backslash (\) and move the cursor down a line.

Place the BASIC cassette into the recorder , rewinding it if

necessary.

NOTE*** The symbol + means hit the "RETURN" key on the keyboard

The symbol + will not, of course, be printed on the

screen.

1. Type C100R *

2. Type . EJWf.EFFFR (don't hit + yet!)

3 . Start the tape

4. Hit +

5. When BASIC is loaded (about 30 seconds) the computer will
print a backslash (\) .

To enter BASIC type EJ?j2f^R^ . The computer will print a few charac-
ters, then, on the next line, print the prompt character >. This
prompt character (>) is used throughout BASIC to signify that the
BASIC is ready for additional commands or statements.

To exit BASIC hit the "RESET" button. This will return control
to the monitor. To re-enter BASIC from the monitor without losing
the previous program, enter BASIC at E2B3^, instead of EJ3f0j2f+.
This is extremely useful when you have unintentionally hit the
"RESET" button while in BASIC. Normally, you should enter BASIC
at E000+ , which clears any previous programs .

It is advisable to make a duplicate copy of Apple BASIC on another
cassette. Exit BASIC as described and:

1.

Type

cipjnu

2.

Type

EJWf.EFFFW (don1 1 hit + yet!)

3.

Start the tape

(Recording)

4.

Hit +.

5. The computer will print a backslash (\) when finished.

READING AND WRITING BASIC PROGRAMS ON TAPE

It is possible to store and retrieve BASIC programs on/from a
cassette tape. To write a BASIC program onto a tape:

1. Exit BASIC as described above.

2 . Type Clj2fj2fR4-

3. Type 4A.00FFW8j2f0.FFFW (don't hit 4- yet!)

4. Start the tape (Recording)

5. Hit K

6. - The computer will print a backslash (\) when completed.

7. Enter BASIC at E2B3.

To read a BASIC program from a tape, the same procedure is used
except an R (for READ) is substituted for each W in line 3 above
and the tape unit is playing instead of recording. Loading a
BASIC program in this manner can be done either prior to loading
BASIC or any time thereafter by first exiting BASIC, loading the
program, and re-entering BASIC at E2B3.

PROGRAM EXECUTION

To review all of the program statements, the LIST command is
used. To execute the program the RUN command is used, which
causes the current program to be executed. Program execution
may be interrupted by pressing any key. BASIC will then output
a "STOPPED AT X" message to identify the point of interruption,
where X is a line number.

NOTE*** A BASIC program can only be interrupted at the conclusion
of a line. Therefore, the program:

10 FOR 1=1 to 10 STEP?: NEXTI
cannot be interrupted. It is good practice to separate
potentially erroneous statements onto different lines to
allow interruption if necessary.

The user may wish to examine or modify some of the program
variables before resuming execution of the program. This can be
done with BASIC commands, which execute immediately. For example,
after interrupting a program, the commands:

PRINT A,B,C,D Will print the values of A,B,C and D
A = 100 Will assign A = 100

PRINT A$ Will print the string A$

To resume execution of a BASIC program after interruption, type:

GOTO X , where X is the line number in the message
"STOPPED AT X". GOTO X will begin execution at line number X
without" re-initializing all variables and strings in contrast to
RUN, which re-initializes everything. Therefore, you must use
GOTO X when resuming execution of the program.

ABBREVIATIONS

The following abbreviations are used in this manual:
expr stands for an arithmetic expression.
var is a variable name (numeric, array, or string),

val is a number between -32161 and 32767 inclusive.
+ indicates the pressing of the RETURN key.

NUMERIC REPRESENTATION

Apple BASIC can represent integers in the range -32767 to +32767
Entered values or calculations which result in values outside
these boundaries will produce the error message ">32767" .

VARIABLES

In Apple BASIC the allowed variables and variable names are:

Variable Name Example

numeric simple variable letter or A, N

letter + digit Al, T6

numeric array variable letter or N, T

letter + digit Bl, T4

character string variable letter + $ A$ , N$

The same letter may be used to name any or all of the above types
of variables in one program.

NOTE*** In Apple BASIC the first element of an array, A(l) is
identical to the simple variable A.

EXPRESSIONS

An expression is a combination of numbers, variables, functions,
and operators that can be, by calculation, reduced to a single
value. The simplest expression is a number. Another simple
expression is a variable name. Simple expressions can be combined
to make arbitrarily complex expressions. Any expression may be
enclosed in parentheses. Operations inside a pair of parentheses
will be performed before any operations outside the parentheses.

ARITHMETIC AND RELATIONAL OPERATORS

-expr negative one (-1) times the value of the expr.

NOT expr 0 if expr is non-zero, 1 if expr is zero.

expr * expr the product of the two expressions.

expr / expr the quotient, truncated to an integer,

expr + expr the sum of the two expressions,

expr - expr the difference of the two expressions.

Relational expressions evaluate to one (1) if the condition is met,
zero (0) if the condition is not met.

expr - expr
expr > expr
expr < expr
expr >= expr
expr <= expr
expr <> expr
expr # expr

expr AND expr
expr OR expr
expr MOD expr

1 if expressions are equal*

1 if first expr greater than second.

1 if first expr less than second.

1 if first expr greater than or equal to second.

1 if first expr less than or equal to second.

1 if the expr are unequal.

1 if expr are unequal, same as <> .

1 if neither expr equals zero.
1 unless both expr equal zero,
remainder left after dividing first expr by second

FUNCTIONS
ABS (expr)

SGN(expr)
PEEK (expr)

RND(expr)
LEN(var$)

has the value of the expr when expr is zero or
positive, and has the value of (-1 * expr) when
expr is negative.

0 if expr is zero, 1 if expr is positive, -1 if
expr negative.

is the value (decimal- between 0 and 255 inclusive)
of the memory location whose (decimal) address is
equal to expr.

if expr is positive - gives a random integer
between 0 and (expr -1) .

if expr is negative - gives a random integer
between 0 and (expr+1) .

returns the value equal to the number of characters
currently assigned to the string whose name is var$

ARRAYS

An array is a set of variables (numbers) assigned to a common

variable name. Each variable of the set is identified by the

name of the array followed by a parenthesized subscript. For

example: A (3) references the third variable (number) of the

array A. Other examples are: A(15) , D(100) , E(X).

In Apple BASIC, the first element of an array, B(l), is identical

to the simple variable B. A reference to element zero (0) or a

negative reference is an error, and will generate the error

message "RANGE ERR".

Declaring arrays is done using a DIM statement, which gives the

name of the array and its DIMensions.

The DIMension of an array specifies the number of variables in an
array (the maximum allowable subscript) . For example:
DIM A (15) , N(6) assigns 15 variables to the array A (A(l) through
A(15)) and six variables to the array N (N(l) through N(6)). There
is no limitation on the number of variables dimensioned for an
array other than restrictions due to available memory. If memory
limitations are exceeded, a "MEM FULL ERR" will result.
NOTE*** Array variables are not initialized to any value.

STRINGS

Apple BASIC provides the user with the capability to manipulate
character strings . A string is a sequence of characters which may
include letters, digits, spaces and special characters (except
quotation marks) . A string literal (constant) is a string enclosed
within quotation marks. String literals are often used in PRINT
and INPUT statements -

100 PRINT "THIS IS A STRING LITERAL"

200 INPUT "X=", X
The quotation marks are not printed with the string. BASIC also
permits the use of string variables. String values are assigned to
string variables using the LET (or Implied LET) and INPUT commands.
Apple BASIC strings function according to the following rules:

1. String variable names must be of the form: letter $ (Z$) .

2. A string is DIMensioned for a maximum length using the DIM
statement of the form: DIM A$(20), B$(100) ...

A string may be DIMensioned to have a maximum length of from 1
to 255 inclusive. If an attempt is made to DIMension a string
outside this range, the error message "RANGE ERR" will result.

3. If it is not specified in a DIM statement, a string's maximum
length is taken to be zero (empty) .

4. A string may contain fewer characters or the same number of
characters as its maximum length, but may never contain more
characters than its maximum length. If an attempt is made to
exceed this maximum length, the error message "STR OVFL ERR"
(string overflow error) will result.

SUBSTRINGS

Program statements using string variables may also use portions
of strings (substrings) by subscripting the string variable name.

Where no subscript is specified, the entire string is referenced.

If one subscript is specified - A$(5) for example - the characters

occupying the 5th (in this case) through the last position

inclusive are referenced.

If two subscripts are specified - A$(2,6) for example - the

characters occupying the positions 2 through 6 inclusive are

referenced.

Any numeric expressions may be used as subscripts. A$(I/J) for

example, references the characters occupying positions I through

J inclusive/ where I and J are evaluated to character positions

in the string and I is less than or equal to J.

For example, assume that A$="ABCDEFG" , then
PRINT A$ yields ABCDEFG
PRINT A$(5) yields EFG
PRINT A$(2,6) yields BCDEF
PRINT A$(l,l) yields A

DESTINGATION STRINGS

A destingation string is a string variable into which a different
(source) string is being copied. Part or all of the destination
string may be replaced by part or all of the source string.
Rules

1. The destination string (to the left of the " = " sign) must be
large enough to hold the source string.

2. If no subscripts are specified (A$=B$) then the entire source
string (B$) replaces the entire string in the destination
variable (A$) . (If the source string is shorter than the
destination string, trailing blanks are appended as necessary)

3. If one subscript is specified for the destination string
(A$(5) = B$) then the destination string, beginning with the

specified character (the 5th character in this case) is
replaced with the source string,

4. Specifying two subscripts (A$(3,5)) for the destination
string is not allowed in Apple BASIC,

5. Zero, one or two subscripts may be specified for the source
string, following the rules listed for substrings.

LEN FUNCTION

The LEN function returns the value equal to the number of charac-
ters currently assigned to a string variable.
Its form is: LEN(X$) .

The length function can be used to link strings together as
follows: B$ (LEN(B$)+1) = A$ . This will assign the characters
from source string A$ to sequential character positions immediately
following the last character previously assigned to the destination
string, B$. The LEN function may be used with any program state-
ment or command which has an expression (expr) argument.

STRING IF STATEMENT

Strings may be used in the relational expression of an IF - THEN
STATEMENT. The logical operators allowed in Apple BASIC for a
string IF statement are = and # (equal and not-equal) . The
strings are compared character by character on the basis of the
ASCII character value. String variables may be subscripted in
an IF statement (IF A$(3,7) = B$(4,8) THEN ...). If characters
in the same positions are identical but one string has more
characters than the other, the strings are considered not-equal.

BASIC INSTRUCTIONS

There are two kinds of instructions in BASIC: Commands and State-
ments. Commands are executed immediately after a + , do not have
line numbers, and are not part of a program. Statements are
always preceded by line numbers and become part of a program.
Statements are executed only during the execution of a program.

Several BASIC instructions can be used both as statements and as
commands . When used as commands , they execute immediately and
are not part of a BASIC program. Used in this manner they can
be useful for immediately examining or modifying program variables
during interruption of program execution. With this feature, the
Apple computer is also a simple calculator able to perform
mathematical calculations immediately, without the necessity of
writing a program. An instruction used as both a statement and
a command:

>10 PRINT A,B This is a statement in a BASIC program. Upon

encountering line 10, a BASIC program will
print the values of variables A and B.

>PRINT A,B This is a command. The current values of A

and B will be printed immediately after a +.

COMMANDS

The following commands (control commands) are used to enter,
examine, modify and run BASIC programs. In addition to the con-
trol commands several BASIC instructions which can be used as
commands are denoted in the list of statements.

AUTO vail, vail starts automatically supplying line numbers.

vail specifies the first line number value
and val2 specifies the increment between
successive line number values. If val2 is
omitted, it is assumed to be ten (10) .
A control D (hitting the control key and D
simultaneously) will terminate AUTO.

CLR sets all variables to zero, cancels any

pending FORs or GOSUBs and undimensions any
array and string variables.

DEL vail, val2

LIST vail, val2

RUN vail

SCR

HIMEM = (expr)

LOMEM = (expr)

erases from the program all lines numbered
from vail to val2 inclusive. If val2 is
omitted , just one line (vail) is DELeted.

displays all program statements on lines
numbered from vail to val2. If val2 is
omitted, just line vail is displayed. If
both vail and val2 are omitted, the entire
program is LISTed.

does a CLR then initiates program execution
beginning at line vail* If vail is omitted,
then program execution starts at the lowest
numbered line.

SCRatches (DELetes) the entire program.
Nothing is saved.

sets the high memory boundary for user pro-
grams (in decimal) . Initializes to 4096.

sets the low memory boundary for user pro-
grams (in decimal). Initializes to 2048.
Both HIMEM and LOMEM destroy any current
user programs.

STATEMENTS

Those BASIC instructions that can also be used as commands are
denoted with a "C" in the left margin.

C LET vav - expr or var = expr (Implied LET)

LET evaluates expr and asigns the resultant value to
vav. Use of the word LET is optional. Variables may
be of any type (string, array, numeric) .

INPUT item

An item may be any kind of variable name (string, array,
numeric) . An INPUT statement may contain several items
separated with commas, each of which must be supplied a
value.

INPUT prints a question mark (?) and awaits the user to
input a value for the variable. A message can be printed
prior to the "?" by preceding the list of variables by a
message (in quotation marks) followed by a comma.
Responses to a multi -variable INPUT statement must be
separated, using either a comma or a \ between each
response. If an INPUT statement contains one or more

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string variables, the responses must be separated with a
+ (commas not allowed) .

Examples: INPUT A

INPUT A,B,C$,D(2)

INPUT "ENTER A, A$ ,8(3) " , A,A$,B(3)

C PRINT item(s)

The item may be any kind of variable name, an expression,
or a message to be printed. A message must be enclosed
in quotes.

Any number of items may be printed using one PRINT state-
ment. The items must be separated by either semicolons
(;) or commas (,). The semicolon indicates that the items
are to be printed with no intervening space. The comma
forces the item following it to be printed in the next
available column position. For this purpose the screen
is thought of as consisting of five columns each eight
characters wide.

A semicolon at the end of a list of items indicates that
tile next PRINT statement to be executed will begin print-
ing exactly where the present one stopped. A terminating
comma is illegal.

Examples: PRINT A,C$,D(2)

PRINT "message" ;A,; "message" ;
PRINT •"A$=";A$;" — END"

C TAB (expr)

Prints the number of spaces equal to the value of expr
(Modulo 256) .

Examples: TAB 20: PRINT "Hello"
PRINT A;: TAB 20:PRINT B

FOR var = exprl TO expr2 STEP expr3

NEXT var

The FOR and NEXT statements form a pair. The FOR state-
ment sets a numeric variable (var) equal to the value of
exprl. Execution proceeds until the statement NEXT var
occurs. At that time if var exceeds the value of expr2
execution continues from the statement following the NEXT
var. If var does not exceed the value of expr 2 then the
value of expr3s is added to var and execution proceeds
from the statement following the FOR. If STEP expr3 is
omitted from the FOR statement, then expr 3 is assumed to
be +1.

Examples: FOR 1= 1 TO 100

' FOR A= 100 TO 1 STEP -5
NEXT I
NEXT I, J

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C IF (expr) THEN statement IF (expr) THEN line number

If the value of the expression is zero no further action
is taken and execution continues with the next statement
following the IF statement. When the value of the
expression is one (1) the statement following THEN is
executed. A line number may also follow a THEN (instead
of a statement) . This instruction can be used as a com-
mand only if the instructions following THEN are also
commands .

Examples: IF A=B THEN C=l

IF (A=B AND C=D) THEN 50
IF NOT (A>4) THEN END

C GOTO expr

GOTO branches to the line number which equals expr.

Examples: GOTO 100
GOTO A
GOTO (A+B/2)

GOSUB expr
RETURN

GOSUB and RETURN form a pair. GOSUB branches to the line
number which equals expr. RETURN causes a branch to the
line following the most recently executed GOSUB. There
may be several conditional RETURNS in a GOSUB loop.

Examples: GOSUB 100
GOSUB A
RETURN

C DIM varl (exprl) , var2 (expr2) ...

DIMensions an array or string named varl to the value
of exprl, an array or string named varl to the value
of expr 2, and so on. String and numeric variables may
be mixed. An array or string may only be DIMensioned
once in a program.

Examples: DIM A (100)

DIM A$(20) ,B$(10) ,C(50)

C REM text

REMark lets the user insert comments in a program without
affecting the execution of the program. The comments
immediately follow the REM statement and are preserved
literally (spaces and all) . REMarks are printed when
listing the program.

Example: REM THIS IS A REMARK

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END

END stops execution of the program.

POKE exprl, expr2

Puts the value of expr2 (decimal- must be between zero
and 255 inclusive) into the memory location (decimal)
whose value is equal to exprl.

Examples: POKE 4,64 stores 64 in location 4

POKE -2048,55 stores 55 in location -2048

(-2048 = D000 (HEX))

CALL expr

CALL does a JSR to the memory location whose address is
equal to the value of the expr (decimal) . This state-
ment links BASIC with assembly language s ub routine s .
An assembly language RTS (return from subroutine) will
return control to the BASIC and execute the next state-
ment.

Examples: CALL 64
CALL A

NOTE*** Apple BASIC allows putting several statements on one

line number. Each statement must be separated using a
colon ( :) .

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APPLE BASIC ERROR MESSAGES

*** SYNTAX
*** > 32767 ERR

*** >255 ERR

*** BAD BRANCH ERR

*** BAD RETURN ERR

*** BAD NEXT ERR

*** >8 GOSUBS ERR
*** >8 FORS ERR
*** END ERR
*** MEM FULL ERR

*** TOO LONG ERR
*** DIM ERR

*** RANGE ERR
*** STR OVFL ERR

*** STRING ERR
RETYPE LINE

Results from a syntactic or typing error.

A value entered or calculated was less
than -32767 or greater than 32767 •

A value restricted to the range 0 to 255
was outside that range.

Results from an attempt to branch to a
non-existant line number.

Results from an attempt to execute more
RETURNS than previously executed GOSUBs.

Results from an attempt to execute a NEXT
statement for which there was not a
corresponding FOR statement.

Results from more than 8 nested GOSUBs.

Results from more than 8 nested FOR loops.

The last statement executed was not an END.

The memory needed for the program has
exceeded the memory size allotted.

Results from too many nested parentheses.

Results from an attempt to DIMension a
string array which has been previously
dimensioned.

An array or string subscript was larger than
the DIMensioned value or smaller than 1.

The number of characters assigned to a
string exceeded the DIMensioned value for
that string.

Results from an attempt to execute an
illegal string operation.

Results from illegal data being typed in
response to an INPUT statement. This message
also requests that the illegal item be
retyped.

A backslash results when more than 128
consecutive characters are entered without
an intervening 4- .

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